This is second hand info and you should talk to Speer before considering it gospel...
There was a member of this forum, or maybe another forum, that talked to Speer's Tech. Dept. and was told that the 135 grain Gold Dot has a velocity window where it performs properly.
The Gold Dot in question works between 800 and 1100 fps, too slow and it won't expand, too fast it comes apart.
The guy in the video just was not getting the velocity needed.
I recommend you run a box of Gold Dots through your gun and see where they're at.
From the video in your post:
Speer Gold Dot 125 gr +P and 135 gr +P are fired from a S&W 638 into gelatin with four layers of denim.
BB calibration: 607 fps, 3.4"
135 gr
Impact velocity: 783 fps
Penetration: 13.8"
Retained weight: 133.8 gr
125 gr
Impact velocity: 752 fps
Penetration: 16.5"
Retained weight: 124.4 gr